When people try to learn languages they are usually doomed to fail, but the main reason for this is not slow progress or boredom. The real killer is that the learning generally gets harder and harder as it goes on. But I want you to stop and think about that for a moment: learning a language really ought to get easier as you go on; not harder. The more of a langauge you understand, the more sense you should be able to make of anything you try to read in it, so how could it possibly get harder? Well, people usually try to learn a language in a class, and teachers typically expect them to take in more and more information in less and less time as they go on, so most people are left behind and end up sitting there for hundreds of hours learning absolutely nothing. It doesn't have to be like that though. There are much better ways to learn.
There are other mistakes that people make, and one of them is learning vocabulary (words) in boring ways, and the same with learning rules of grammar. When you learn your first language as a young child, you don't make these mistakes, so why would you want to make them now when learning your second language? Don't do it the wrong way, but follow the path of least resistance instead. Learning languages is primarily a matter of memorising lots of words, phrase structures and grammatical rules, but you don't need to put any effort into learning these things. Let the brain do what it's good at by allowing it to decide for you when it should learn a word or rule. Think about how children learn their first langauge: they pick it up almost by accident. I want you to pick up your second language almost by accident too. Don't stare at boring lists of words for hours every day, but sit back instead and let the words flow past you many times while you concentrate your efforts on trying to understand what is being said. The words should come at you through interesting texts which are worth reading in themselves, so learning words from them becomes something that happens by accident as you go along. Don't try to memorise anything, but just let the words write themselves into your memory in their own time. By doing this, the words that come round the most often will fix themselves in your head first, but it also makes sure that they are stored in the brain in the right places; forced learning stores words in the wrong place where access to them is slow.
Step one - get a language course.
There are many different kinds of language course available, some costing a fortune, but others are much more affordable. Some expensive ones aren't very good, while some inexpensive ones are excellent, so how then can you tell which one you should get? Well, it isn't easy, and they keep changing them too, so it's hard to recommend any specific course as the quality keeps going up and down. If a course comes in the form of CDs, you can't look through it before buying it, so it's easy to end up spending a lot of money on something completely useless. The safest thing to do is start out with a book, ideally one with a CD attached to it, though it's a good sign if the book is also available without the CD because that suggests that it doesn't need it to teach the language. Working from CDs is actually a slow way to learn, but they are good at helping you with pronunciation and at giving you practice with trying to understand spoken language. They are also good for people who struggle with reading and for people who spend a lot of time driving cars. If you try to rely on nothing but CDs though, your pronunciation may end up being very poor because you will probably mishear a lot of words and say them wrongly, just like children do when they say "skellington" instead of "skeleton". It is much more efficient to work from a book, so getting hold of a good one should be your first move, and you might find that you never need to buy any CDs at all.
How do you know if a book is good? Well, the best ones always contain lots of texts in the language you're learning, and they provide translations of them all too. Most of the learning you do will take place when you try to read those texts, and you will learn at high speed because you can compare them with the translations whenever you get stuck without ever having to look any words up in a dictionary or vocabulary list. The worst books do not give you any translations of texts, but instead provide you with lots of vocabulary lists, and the further you get through the book, the more of these ghastly lists you have to hunt for and hunt through whenever you can't remember what a word means. The absolute worst of these books don't even bother to put these word lists in alphabetical order, so if you work with one of those bad books you are forced to spend hundreds of hours beavering away while learning next to nothing at all; you're wasting all your time looking up words instead of learning. So, you're looking for a book with lots of texts, ideally interesting ones, and with translations of them all. Many books have lots of random sentences instead of interesting texts, and those will drive you mad. Good texts that are worth reading are important, and you can tell from the translations whether they are or not.
There are a lot of lightweight books which don't do the job properly, so you're looking for something that will introduce you to something approaching a thousand words, and it should explain most of the grammar of the language along the way, but you don't need to try to learn the rules. All you need to do is try to understand them as you go along, and you can keep looking back to see how they work if you forget. Avoid books that are dominated by topics which are likely to bore you. Food is one of the worst topics as it will bombard you with boring vocabulary that you don't want to waste time on at an early stage of learning. Look at books from the "Teach Yourself" range, and look at the books from Routlage too - most of the books I've learned languages from come from these two companies, but there are other publishers which can be better for some languages, so always check out what's on offer from Berlitz, Hugo's, and anything else a good bookshop has on the shelf. If you can afford to, buy two different books, aiming to get the best two, because there is no harm in reading through both of them, either alternating between them or using the second one as revision after working through the first. The first book may have a part in it that is difficult to work past because it fails to explain something properly, so in such a situation you can switch to the other book and work from that instead - this usually overcomes the problem, and then you can go back to the other book later, by which time the problem will be gone. How to use the book: do not blindly do everything that the book tells you to do, because it will probably ask you to try to make up sentences in the language you're learning. There is no harm in doing what it tells you to do later on when you read the book again from the beginning, but you should only do that after you've already read the whole way through it at least once. On your first read through it you do nothing but try to understand and only try to translate from the language you're learning into English. Don't waste time writing lots of things out, but you can often improve a book of this kind by writing little notes into it with a pencil whenever it falls short.
Some languages take longer to learn than others, and it helps a lot if they are similar to the language you already speak, so for an English speaker it is a good plan to have a go at learning another European langauge. Spanish is a particularly good choice for this, but if you're more keen to learn French, Italian or German, go for that instead. Exotic languages like Swahili, Chinese and Japanese are fun, but the words take longer to stick in your head, and the word order used in Japanese takes a lot of time to get used to. I would strongly recommend that you learn one of the European languages I mentioned first, because you will learn so much about learning languages in the process that you'll probably find you can learn both Spanish and Japanese in the same amount of time as learning just Japanese on its own. Your aim should be to race through the book in a reasonably short time, understanding all the texts as you go, aided by the translations and explanations of grammar. Read the texts out loud, or whisper them - the CD, if there is one, will help you with this, but otherwise you will have to rely on the pronunciation guide at the start of the book (which you should read anyway - some of them go on for many pages and it can be a real drag working through it, but it pays off if you do). Whenever it gets too hard, simply go back to the start and race through it again - you'll be amazed at how easy it is to get through it the second time, and you'll be ready to move on again. Once you've learned a few languages, you can get this down to a fine art and read through a course for a new language in about twenty hours, but expect it to take a lot longer the first time - expect it to take three or four months. By the time you've reached the end, you're ready for step two.
Step 2 - read a book in the language.
You can, if you want, go back to the start of the language course and work through it again, this time trying to do the exercises that ask you to translate from English into the language you're learning or to answer questions in that language, but I would advise you not to do this yet. Hold off until you have a much better feel for the language. If you can get to the point where you understand the language well enough to make sense of a novel written in it, you will be able to learn to create your own sentences in that language much more easily, and the sentences you produce will be closer to the kinds of sentences actually spoken by native speakers. You need to get used to the word order they use in sentences and not just string words together in the order they come in in English. So, I want you to be patient and not rush into trying to speak the language. You need to get an interesting book written in the language you're learning, and ideally you want to find one that you can get hold of in English as well, because you will be using that most of the time to save time by avoiding the need to look up a dictionary. Your aim will be to use the English version of the book as little as possible, but you will initially find that you need it all the time. Bit by bit, you will find that you can read longer and longer chunks without needing to consult it.
If you can't get hold of an English version of the book, you can use a dictionary instead, but progress will be very slow at first. Even so, I have worked this way myself. To begin with, I would be looking up the dictionary a hundred times per page, but by the end of the book I was able to read whole pages without looking up the dictionary at all, though I had to guess at the meanings of one or two words to do this. It is massively faster to work with a translation of the book instead of a dictionary, so save yourself a lot of unnecessary work and get something that's available in both languages. Holding two books open at the same time is awkward, but ebooks will make things a lot easier for you - you can either use an ebook reader for one copy of the book and have a paper copy of the other, or, if you have enough of them, use two ebook readers. As to the kind of book to look for, the best ones to start with would be dialogue-rich novels written for children (the kinds of things written for ten-year-olds). These will provide you with all the most important words and phrases the most often, guaranteeing that you pick them up in much the same order as a native speaker does as a child.
Some languages are much more difficult to work with than others because they have awkward writing systems. Chinese and Japanese are particularly hard to make progress with once you've left the safety of your introductory course. It's easy enough when everything's written in the same letters used by English, but when you try to find a book to read you then hit a brick wall because they're all written in in Chinese characters (which the Japanese call kanji). There is a partial solution to this, and that is to read electronic texts on a computer. The Firefox browser is able to use a program called Rikaichan to help you read Japanese writing, but it's still extremely hard to make sense of it even with that software. However, there is a trick you can use with Google translate which can turn everything into English letters for you, and that is to translate from English into Japanese, but paste the Japanese text you want to translate into the English side instead of the Japanese side - this will result in the Japanese text appearing on the Japanese side with the Japanese put into English letters underneath. Now, the output isn't perfect as words can be chopped up wrongly, but it's much easier to work with than the Chinese characters and Japanese symbols on their own, so you'll be able to read all the words you already know straight away, and it will help you line up the mouse cursor on the right characters in the proper Japanese version of the text to get more efficient use out of Rikaichan. You will find that working this way will also gradually help you to learn to read the Japanese writing over time too. A good collection of Japanese texts can be found at http://etext.lib.virginia.edu/japanese/texts/index.html .
Step 3 - learn to create sentences.
Now you're ready to try to create your own sentences in the language you're learning. You now own the language, so you can learn to speak it from a position of power. Work through your language course again, this time doing all the exercises in the way the book tells you to do them. Speak to people in the language too if you can. There are places like livemocha on the internet where you can have conversations (through text) with people who speak the language you're learning, so you don't need to spend money to do this (beyond having basic internet access).
Step 4 - spread the word about this method of learning languages.
In an ideal world, lots of good reading material would be made available in
the right form for learning languages by this method. There are a few books
available for some languages with "parallel texts" where every line of text
has an English translation underneath it, or where every second page is a
translation of the page before it, but there aren't enough of them and they
aren't done properly. What's needed is to have (1) a line of text in the
language you're learning, (2) then, if it uses a different script, a line
repeating it in English letters, (3) then, if the pronunciation can't be
worked out from the normal spelling, a line of text showing the
pronunciation, (4) then a line of text giving a literal translation where
English words are used but maintaining the original word order, (5) then a
line of English giving the full translation. Once such books are available,
language learning will be transformed, becoming much easier, faster and